Effects of the Glucosinolate Sinigrin in Combination With a Noniodine Supplemented Diet on Serum Iodine and Thyroid Hormone Concentrations in Nonpregnant Mares

Exposure to plants containing glucosinolates (GSLs) affects thyroid function in many species, in horses is implicated in the birth of foals with congenital hypothyroidism. The present study was performed to determine the effect of feeding a GSL (sinigrin) in combination with a low-iodine diet for 12 weeks on thyroid hormones and serum iodine concentrations in nonpregnant mares. Nineteen mares aged 2–14 years were divided into control (n = 6), low (20 mmol/day) (n = 7) and high GSL (35 mmol/day) (n = 6) groups. Thyrotropin-releasing hormone (TRH) stimulation tests and serum iodine measurements were performed at 0 and 12 weeks. Total triiodothyronine (TT3), total thyroxine (TT4), and thyroid-stimulating hormone (TSH) concentrations were measured at the baseline and in post-TRH samples. The post-TRH value minus the basal value (Delta Δ) and fold change (FC) were calculated for TSH, TT3, and TT4. Data were analyzed at P < .05. Highlights included Delta Δ and FC TT4 and TT3 concentrations having a group and week interaction (P < .001) with week 12 control mares having higher values than mares in week 12 low and high GSL groups. TT4 FC values had a group (P < .001) and group by week interaction (P < .001) with week 12 control concentrations higher (P < .006) than all groups. Iodine concentrations decreased (P < .002) over time in GSL mares. In conclusion, feeding mares a low-iodine diet with 20 and 35 mmol sinigrin/day resulted in lower serum iodine concentrations.     

Markers for Predicting Overweight or Obesity of Broodmares

Obesity has become of great concern to all equine community from both veterinary and welfare points of view. For estimating obesity markers of brood mares, 17 mares with body conditions were subjected to blood sampling and ultrasound examination to measure rump fat for 6 consecutive weeks. Body length (L), girth (G), and height (H) were measured to estimate body weight (BW), body fat %, body fat mass (BFM) and body mass index (BMI). Mares were classified into three groups according to body condition score (BCS) and rump fat thickness (RF). Overweight mares (O) had BCS >7 and RF >7 mm, moderate (M) had BCS and RF >3 to ≤7, and emaciated (E) had BCS and RF ≤ 3 mm. Glucose, triglycerides, nitric oxide (NO), insulin, insulin-like growth factor-I (IGF-1), leptin, ovarian hormones, and thyroid hormones were measured. Results revealed that BCS, G, L, L × G × H, BW, RF, fat %, and BFM correlated significantly (P < .0001) with body condition. Tetraiodothyronine concentrations of E mares were significantly high (P = .04), but triiodothyronine concentrations tended (P = .07) to be low. Insulin (P = .06) and IGF-1 (P = .07) concentrations tended to be high in O mares. Moderate mares had the highest leptin concentrations (P = .007), but E mares had the lowest P4 concentrations (P = .01). Overweight mares had nonsignificantly high glucose, NO, and triglycerides. In conclusion, back fat and morphometric measurements are the easiest and simple assessment of overweight and obesity. Obese and overweight mares showed slight hyperinsulinemia, hypertriglyceridemia, and hyperglycemia. Hyperleptinemia alone is not indicative of obesity.     

The Potential Role of Training Sessions on the Temporal and Spatial Physiological Patterns in Young Friesian Horses

This study compares the circulating adrenocorticotrophin hormone (ACTH), cortisol, lactate, glucose, heart rate, respiratory rate, rectal temperature, and blood count values in initially 2-year-old horses subjected to dressage training schedule during three consecutive days per 2 weeks. Sixteen healthy Friesian horses were used and were considered dressage group. Six healthy young horses not involved in training programs were used as control group. Blood sampling were collected from the jugular vein in baseline condition (dressage group and control group) and after exercise, within 5 minutes of the end of the training session (dressage group). Compared to baseline values, results showed higher ACTH concentrations after the first day of the first training week (P < .005) and after the third day of the second week (P < .005); higher lactate concentrations after the second and the third day of the second week (P < .01); lower glucose concentrations after the third day of the first week (P < .01); higher HR, RR, and RT values and lower PLT count after different time points during both training weeks. One-way ANOVA showed significant training effect for ACTH (F = 7.605; P < .0001) and glucose (F = 3.505; P < .001) concentrations over time points. Two-way ANOVA showed a significant effect of dressage training sessions between the first and the second week for ACTH (F = 6.508; P < .001) and cortisol (F = 5.559; P < .0001) concentrations. From obtained data, it seems that the use of ACTH and cortisol changes for the assessment of effects of training in initially 2-year-old horses could be an ideal measure of quantitative and qualitative stress responses. The quantification at the same time of functional responses to stressful stimuli may offer a more objective measurement of dressage training effects.     

Effects of vitamin E and selenium administration on pregnant,heavy draft mares on placental retention time and reproductive performance and on white muscle disease in their foals

This study investigated the effects of administering vitamin E and selenium to pregnant heavy draft horsemares on the incidence of retained placenta and postpartum reproductive performance and on the prevention of the white muscle disease in their foals. In study A, 1,000 mg of vitamin E and 50 mg of selenium (E-SE 20 mL) were given to 22 mares 3 weeks before expected parturition (335 days counted from last mating), whereas 28 mares were used as controls. In study B, E-SE were administered 2 weeks before expected parturition at 2 dose levels, with 25 mares receiving 20 mL E-SE, 19 mares receiving 10 mL, and 29 mares kept as controls. Vitamin E and selenium were assayed in serum collected from some of the mares before administration of E-SE and again postpartum and from the foals immediately after birth. Serum selenium concentrations before E-SE administration were deficient (<65 ng/mL) in all mares (n = 48) but were increased in the postpartum sample from treated mares regardless of the dose or timing of administration (n = 31) (P = .05). Only study B mares were deficient in vitamin E prepartum, and both dose levels of E-SE had corrected this in the postpartum sample (P = .01). All foals were selenium deficient regardless of whether their dams had received E-SE or not, although concentrations were higher in foals from treated study A mares than from controls (P = .05). Mares with the highest selenium concentrations prepartum (40 ng/mL and over) had shorter placental retention times than mares with lower selenium concentrations (P = .05) and did not respond to E-SE with a further reduction in retention time. By contrast, mares with prepartum selenium concentrations between 20 and 40 ng/mL tended to respond to E-SE with a shortened placental retention time (P = .07). E-SE administration reduced the mean number of days from parturition to last mating (nonpregnant term) in study B mares (P = .05) and in mares with adequate prepartum vitamin E concentrations (>300 g/mL, P = .05). We conclude that maintaining high level serum vitamin E and selenium concentrations of prepartum mares is expected to increase fertility of selenium-deficient mares. Therefore, the regimen of vitamin E and selenium administrations to selenium deficient mares should be developed.     

The Role of Equine Chorionic Gonadotropin in the Stimulation of Luteal Steroidogenesis in Mares Carrying Horse or Mule Pregnancies

The stimulatory role of equine Chorionic Gonadotropin (eCG) in the production of steroid hormones was evaluated during the first 4 months of pregnancy in mares impregnated by either stallions or jack donkeys. Twenty mares were divided in two groups: Mares in the first group were inseminated with stallion semen (horse pregnancies), and those in the second group were inseminated with donkey semen (mule pregnancies). Blood samples were collected twice weekly from day 30 to day 120 of pregnancy to determine the concentrations of eCG, progesterone, androstenedione, and testosterone. Analysis of variance for repeated measures was used to compare the concentrations of each hormone between groups. Linear regression models that considered the linear and quadratic effects of week of gestation as well as the linear and quadratic effects of the concentrations of eCG on the production of each steroid hormone were carried out. Concentrations of eCG, progesterone, and androstenedione were higher in horse than in mule pregnancies (P < .01 for eCG and P < .05 for progesterone and androstenedione). Testosterone concentrations were also higher in horse pregnancies than in mule pregnancies at weeks 7, 9, and 10 (P < .05). Regression analysis indicated that eCG had considerable stimulatory effects on the secretion of progesterone and androstenedione and weaker effects on the secretion of testosterone. The results suggest that eCG stimulates luteal production of progesterone, androstenedione, and testosterone in horse and mule pregnancies, these effects being more evident in horse pregnancies than in mule pregnancies due to the higher concentrations of eCG in horse pregnancies.     

Changes in plasma melanocyte-stimulating hormone,ACTH, prolactin,GH, LH,FSH, and thyroid-stimulating hormone in response to injection of sulpiride,thyrotropin-releasing hormone,or vehicle in insulin-sensitive and -insensitive mares

Six insulin-sensitive and 6 insulin-insensitive mares were used in a replicated 3 by 3 Latin square design to determine the pituitary hormonal responses (compared with vehicle) to sulpiride and thyrotropin-releasing hormone (TRH), 2 compounds commonly used to diagnose pituitary pars intermedia dysfunction (PPID) in horses. Mares were classified as insulin sensitive or insensitive by their previous glucose responses to direct injection of human recombinant insulin. Treatment days were February 25, 2012, and March 10 and 24, 2012. Treatments were sulpiride (racemic mixture, 0.01 mg/kg BW), TRH (0.002 mg/kg BW), and vehicle (saline, 0.01 mL/kg BW) administered intravenously. Blood samples were collected via jugular catheters at −10, 0, 5, 10, 20, 30, 45, 60, 90, and 120 min relative to treatment injection. Plasma ACTH concentrations were variable and were not affected by treatment or insulin sensitivity category. Plasma melanocyte-stimulating hormone (MSH) concentrations responded (P < 0.01) to both sulpiride and TRH injection and were greater (P < 0.05) in insulin-insensitive mares than in sensitive mares. Plasma prolactin concentrations responded (P < 0.01) to both sulpiride and TRH injection, and the response was greater (P < 0.05) for sulpiride; no effect of insulin sensitivity was observed. Plasma thyroid-stimulating hormone (TSH) concentrations responded (P < 0.01) to TRH injection only and were higher (P < 0.05) in insulin-sensitive mares in almost all time periods. Plasma LH and FSH concentrations varied with time (P < 0.05), particularly in the first week of the experiment, but were not affected by treatment or insulin sensitivity category. Plasma GH concentrations were affected (P < 0.05) only by day of treatment. The greater MSH responses to sulpiride and TRH in insulin-insensitive mares were similar to, but not as exaggerated as, those observed by others for PPID horses. In addition, the reduced TSH concentrations in insulin-insensitive mares are consistent with our previous observation of elevated plasma triiodothyronine concentrations in hyperleptinemic horses (later shown to be insulin insensitive as well).     

Exercising the Pregnant Mare from Day 16 to Day 80 of Gestation

Our previous research has demonstrated moderate exercise can be detrimental to early pregnancy in the mare, but little work has examined exercise after pregnancy has been detected. We exercised mares (n = 8) 6 days a week for 45 min from Day 16 until Day 80 of gestation. Color Doppler ultrasonography was used to evaluate embryonic vesicle size, fetal length, and uterine blood flow. Blood was sampled every other day to analyze cortisol and progesterone concentrations. Results indicated that exercising pregnant mares (n = 4) led to greater (P < .01) cortisol concentrations 30 min after the exercise period. No overall treatment effect could be detected in progesterone concentrations; however, following Day 60 of gestation, progesterone concentrations were lower (P < .05) in exercised mares. Additionally, progesterone concentrations peaked earlier in exercised mares at Day 52 of gestation compared to peak levels at Day 68 of gestation for control mares. No significant effects were detected in embryonic vesicle size. Fetal length tended (P = .06) to be longer in the conceptus of exercised mares. Uterine blood flow did not differ between groups but increased as pregnancy progressed (P < .001) in both groups. All mares in this study went on to deliver healthy foals and suffered no difficulties during parturition. These results indicated that moderate exercise was not detrimental to mare pregnancy.     

Use of Acupuncture to Induce Cyclicity in Anestrous Mares

Acupuncture is part of an Eastern system of medicine used for diagnosing, treating, and preventing disease. It has been used for the treatment of reproductive disorders in both human beings and domestic species. We hypothesized that acupuncture could be used to induce cyclicity in anestrous mares. In experiment 1, six anestrous mares were treated with acupuncture at Bai Hui, governing vessel (GV)-2, bladder (BL)-22, BL-23, BL-31, and BL-33 twice a week for 3 weeks, then once a week for an additional 8 weeks, whereas six anestrous mares served as controls. In experiment 2, six anestrous mares received acupuncture stimulation at Bai Hui, GV-1, BL-22, BL-23, and BL-28, with electroacupuncture (10 minutes at 50 Hz) at BL-22 and BL-28 bilaterally. In addition, vitamin B12 (3 mL, 1,000 mcg/mL) was injected in the vaginal fornix at the 3, 6, and 9 o’clock positions around the cervix. Six anestrous mares served as controls. Examinations and treatments were carried out twice a week until ovulation. In both experiments, ovarian activity was examined in all mares by transrectal ultrasonography and blood sample was obtained twice a week to determine progesterone concentrations. The time to first ovulation for experiment 1 was 14.0 ± 0.7 and 13.5 ± 1.0 weeks (mean ± SD) for the control and acupuncture groups, respectively (P = .60). In experiment 2, the time to ovulation was 9.0 ± 0.6 and 10 ± 0.3 weeks (mean ± SD) for the control and acupuncture groups, respectively (P = .19). No significant difference was found between the treated and control mares in either study.     

Effects of recombinant equine growth hormone on in vitro biomechanical properties of the superficial digital flexor tendon of Standardbred yearlings in training

OBJECTIVE: To determine whether recombinant equine growth hormone (rEGH) would alter the in vitro biomechanical properties of the forelimb superficial digital flexor tendon (SDFT) in exercising young Standardbred horses. STUDY DESIGN: Randomized complete block design. ANIMALS: Twelve Standardbred yearlings. METHODS: Horses were trained for 12 weeks on a high-speed treadmill (10% positive incline). rEGH was administered intramuscularly (IM) daily (10 microg/kg during week 4; 20 microg/kg for weeks 5-9) to 6 horses (treated group), whereas 6 horses (control group) were administered an equivalent daily volume of sterile water IM. At 12 weeks, horses were euthanatized and left forelimb SDFTs were collected and stored (-70 degrees C). A section from the mid-region of the SDFT was held in cryoclamps with a 4 cm interspace distance and distracted at 10 mm/s until failure. The variables evaluated were maximal load at yield and failure, ultimate and yield tensile stress and strain, tendon stiffness, and mode of failure. Data were analyzed using unpaired, two-tailed, Student's t-test. Statistical significance was set at P < or =.05. RESULTS: Yield and ultimate tensile stress were significantly lower in the rEGH-treated horses compared with controls. There was a trend toward increased maximal displacement, increased ultimate tensile strain, and decreased tendon stiffness in rEGH-treated horses compared with controls. Tensile stress and cross-sectional area, and tensile stress and stiffness were significantly correlated at yield and failure points. CONCLUSIONS: rEGH, administered at the manufacturer's recommended dose rates to maturing Standardbred horses in training, does not significantly augment the in vitro biomechanical properties of the forelimb SDFT. CLINICAL RELEVANCE: Administration of rEGH to young horses in training is unlikely to enhance the physiologic adaptation of the SDFT to exercise stress.     

Absorption of Different Oral Formulations of Natural Vitamin E in Horses

The objective of this study was to determine the effect of vitamin E source on plasma vitamin E concentration. Five different formulations of natural source vitamin E (4,000 IU/day) were supplemented to Standardbred mares (n = 4 per group) for 14 days. Treatment 1 was given 10 g of 400 IU/g natural acetate (RRR-α-tocopheryl-acetate) powder, treatment 2 was given 6.66 g of 600 IU/g natural acetate powder, treatment 3 was given 6.66 g of 600 IU/g natural alcohol (RRR-α-tocopherol) powder, treatment 4 was given 20 g of 200 IU/g micellized natural alcohol powder, and treatment 5 was given 8 mL of 500 IU/mL micellized natural alcohol liquid. Blood samples were collected before supplementation (day 0), after day 7 and day 14 of supplementation, and analyzed for plasma α-tocopherol. Treatments 1, 2, and 3 increased (P < .05) from days 0 to 7, but remained similar at day 14. Treatments 4 and 5 also increased (P = .004, and P < .0001, respectively) from days 0 to 7 and were higher (P < .05) than treatment 1, 2, and 3. Plasma levels peaked at day 7 and either plateaued or decreased (treatment 5, P = .004) at day 14. The micellized alcohol formulations remained elevated (treatment 4) or decreased (treatment 5) after achieving peak blood concentration and, as hypothesized, tended to have plasma concentrations higher than the other vitamin E forms. Care should be taken to ensure that the most active biologically available form of vitamin E is provided in the diet to maximize its efficiency.     

Chronic clenbuterol administration alters myosin heavy chain composition in standardbred mares

The purpose of this study was to examine changes in myosin heavy chain (MHC) composition due to chronic clenbuterol administration with or without exercise in mares. Unfit Standardbred mares (aged 10+/-3 years) were divided into four groups: clenbuterol (2.4 micro/kg BW twice daily) plus exercise (3 days/week for 20 min at 50% VO(2max); CLENEX; n=6), clenbuterol only (CLEN; n=6), exercise only (EX; n=5), and control (CON; n=6). Muscle biopsies were obtained from gluteus medius muscle before and after the eight-week training/administration period. MHC composition was determined via SDS gel electrophoresis and quantified using a scanning and densometric system.CLENEX and CLEN exhibited significant (P<0.05) MHC changes while EX and CON did not. MHC type IIA decreased (29.8+/-6.1 to 19.3+/-4.0%, CLENEX; and 36.8+/-12.4 to 26.4+/-7.9%, CLEN) and MHC type IIX increased (59.4+/-7.2 to 71.8+/-5.8%, CLENEX; and 50.5+/-12.5 to 62.0+/-9.3%, CLEN). Chronic clenbuterol administration with and without exercise resulted in a significant shift in MHC profile in Standardbred mares.     

Effect of dose of furosemide on plasma tCO2 changes in standardbred horses

Nine Standardbred horses of similar athletic fitness (six mares, three geldings), ranging from 4 to 11 years of age, were used to determine the effects of 0, 250, or 500 mg intravenously administered furosemide on plasma tCO₂ changes over time. All horses were either currently racing or in advanced stages of race training before entering a qualifying race. Horses were randomly allotted to one of the three treatment levels of furosemide during 3 consecutive weeks. Jugular venous samples were obtained from horses at rest in box stalls before and hourly for 6 hours after administration of furosemide. Body weights of horses ranged from 356 to 456 kg, and the mean was 417 kg. Thus, the dose of furosemide received by each horse ranged from 0.55 to 0.70 mg/kg body weight for the 250-mg injections and from 1.1 to 1.4 mg/kg body weight for the 500-mg injections. Furosemide caused metabolic alkalosis in the horses. Least square means (±SEM) were determined and horses had adjusted plasma tCO₂ of 32.2, 33.9, and 34.7 ± 0.41 for the 0-, 5-, and 10-mL doses of furosemide, respectively. The type 3 tests of hypotheses found that there was a difference (P < .0001) across time, a difference (P = .0016) according to furosemide dose, and a difference (P < .0001) according to treatment × hour. There was no difference (P > .05) according to week or treatment × week. These data suggest that either 250 or 500 mg furosemide given to Standardbred race horses induces statistically similar metabolic alkalosis.     

Hyperleptinemia in Mares: Prevalence in Lactating Mares and Effect on Rebreeding Success

Previous research from our laboratory showed that approximately one third of obese, nonfoaling mares displayed a condition of hyperleptinemia coupled with hyperinsulinemia that resembled type 2 diabetes in humans. The current study was performed to evaluate the prevalence of the hyperleptinemic syndrome in lactating mares and its possible impact on their rebreeding success. Additionally, we investigated possible relationships between leptin levels in lactating versus nonlactating mares. In experiment 1, jugular blood samples were collected from 198 lactating mares on two occasions approximately 2 weeks apart. The mares resided on eight farms in Louisiana; breeds included Thoroughbred (n = 86), Quarter Horse (n = 71), Warmblood (n = 24), and draft-type (n = 17). Body condition scores (BCS) were measured at the time of blood sampling; plasma samples were assessed for leptin and progesterone concentrations. Reproductive and medical histories, as well as feeding regimens, were compiled on each mare. Based on our previous reports and examination of the current data, a mare was considered hyperleptinemic if her plasma samples contained greater than10 ng/mL leptin; normal was considered 6.0 ng/mL or less; mares with levels above 6.0 and 10 ng/mL or greater were classified as intermediate. Overall mean leptin concentration was 4.7 ng/mL, and average BCS was 5.5. After analysis, 24 mares were classified as hyperleptinemic (12%), 138 were classified as normal (70%), and 36 were classified as intermediate (18%). Leptin concentrations were affected by BCS (P = .08), with higher concentrations in mares with higher body condition; however, there were hyperleptinemic mares with BCS of 4 to 5.5. Feeding regimen affected leptin concentrations (P < .01), with mares on pasture full-time having the highest concentrations. There was no effect of breed, mare age, number of years the mare had been bred, number of live foals, progesterone concentrations, or last foaling date on leptin concentrations. Rebreeding success averaged 81% overall and was not affected by leptin classification. In experiment 2, nonfoaling mares kept on pasture had mean leptin concentrations of 7.0 ng/mL; 8 of 31 mares (26%) displayed hyperleptinemia. Mean leptin concentration was correlated with BCS (R² = 0.65; P < .02) but was not affected by age of the mare. It was concluded that the hyperleptinemic condition occurs in lactating broodmares, even at BCS as low as 4. The overall incidence appears to be lower in broodmares than in nonfoaling mares, likely because of their lower BCS in general and the energy demands of lactation. Hyperleptinemia did not affect rebreeding success at the end of the breeding season.     

Leptin and Ghrelin and the Indices of Lipid Metabolism as Related to Sex Steroid Hormones in Trotters

This study examined the influence of sex steroid hormones on lipid metabolism in horses. The group of 34 clinically healthy Standardbred trotters aged 2 to 4 years was studied during an exercise test. The horses were divided into groups according to their sex. These groups were: 11 stallions, 16 mares, and seven geldings. Concentrations of testosterone, 17-β-estradiol, leptin, ghrelin, glycerol, free fatty acids (FFA), and triacylglycerols (TG) were measured in plasma obtained from blood samples taken at rest and after the end of the exercise. At rest, plasma ghrelin concentration was significantly higher in geldings than in stallions and mares (1,541 ± 206 vs 1,280 ± 288 and 1,310 ± 267 pg/mL, respectively; P = .012). Leptin was lower in geldings than in mares (2.65 ± 0.93 vs 4.70 ± 2.31 ng/mL; P = .036). The post-exercise rise in plasma ghrelin and TG concentrations was significantly higher in mares than in geldings (+220 ± 330 vs -25 ± 206 pg/mL; P = .049 and 0.31 ± 0.14 vs 0.13 ± 0.15 mmol/L; P = .016, respectively). The increase in plasma FFA level was higher in geldings than in stallions (535 ± 178 vs 334 ± 191 μmol/L, P = .046). In conclusion, lipolysis rate in geldings is higher than in noncastrated trotters.     

Age-Dependent Effect of Foal Heat Breeding on Pregnancy and Embryo Mortality Rates in Thoroughbred Mares

The aim of the present study was to evaluate the correlation of age and heat cycle to determine reproductive efficiency in young and aged Thoroughbred mares bred on foal heat (FH) or on second heat (SH) after foaling. Embryo mortality (EmbM) was determined every time a mare was found open after a positive pregnancy diagnosis. Parturition to breeding interval, pregnancy rate (PregR) and EmbM rate were the dependent variables and the treatments were breeding on the FH or on SH. The cutoff age to obtain above-average probability for the EmbM was 10 years old. PregR in mares bred on FH was lower compared with SH (P < .01); however, it was neither affected by the age of mares (P > .05) nor by the age group of mares (P > .05). Regarding FH and SH, there was a difference in PregR in young mares (P < .01), unlike in aged mares (P > .05). EmbM rate was not different between mares bred on FH or SH (P > .05) although it was affected by age of mares (P < .01). EmbM was higher in oldest than young mares (P < .01). Aged mares bred on FH had a significantly higher EmbM rate compared with the young group also bred on FH (P < .01). In conclusion, the reproductive efficiency of Thoroughbred mares bred on FH is dependent of the age. Aged mares (≥10 years old) should be bred at their SH to reduce EmbM and improve reproductive performance.     

Factors Affecting the Glucose Response to Insulin Injection in Mares: Epinephrine, Short- and Long-Term Prior Feed Intake, Cinnamon Extract, and Omega-3 Fatty Acid Supplementation

Five experiments were conducted with mares to better define factors that might affect the assessment of insulin sensitivity via direct insulin injection, and to then apply this method of assessing insulin sensitivity to trials which tested two potential supplements for improving poor insulin sensitivity in horses. The experiments assessed the effects of the following: (1) previous administration of epinephrine, (2) overnight feed deprivation versus hay or pasture consumption, (3) 10-day acclimatization to hay in a dry lot versus pasture grazing, (4) cinnamon extract supplementation, and (5) fish oil supplementation on insulin sensitivity. Mares of known high and low insulin sensitivities were used in the first three experiments, whereas mares with low insulin sensitivities were used in the supplement trials. Epinephrine administration increased blood glucose concentrations (P < .05) and prevented the insulin-induced decrease in blood glucose concentrations in both sensitive and insensitive mares. Overnight feed deprivation decreased (P < .06) insulin sensitivity relative to overnight ad libitum access to hay, and both regimens resulted in reduced insulin sensitivity relative to overnight pasture availability; sensitive and insensitive mares responded similarly except when kept on pasture (P = .0854). Ten days of hay consumption in a dry lot reduced (P < .05) insulin sensitivity in insensitive mares, but not in sensitive mares, relative to pasture grazing. Supplementation with cinnamon extract or fish oil had no effect on insulin sensitivity of mares with known low insulin sensitivity under the conditions of these experiments.     

Lipid Utilization Pathways Induced by Early Training in Standardbred Trotters and Thoroughbreds

Controversial results on lipid utilization as an energy source during training in horses are found in the literature. The objective of this study was to assess blood lipid profile during different training programs in horses. Seventeen Standardbred horses (400 ± 50 kg) and 17 Thoroughbred horses (380 ± 15 kg) followed different training programs. Blood lipid profile, including triglycerides (TGs), total cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL), was analyzed, and very-low-density lipoprotein (VLDL) concentration was calculated. Data were analyzed using Student t test, and linear regressions were done. Cholesterol and LDL decreased during training programs in Standardbred trotters (P = .0001 and P = .0053, respectively), and VLDL was found to be close to the significance level (P = .053). Blood lipid profile, including TGs (P = .0014), cholesterol (P = .0057), HDL (P = .0128), LDL (P = .0091), and VLDL (P = .0014), varied throughout the training program in Thoroughbred horses. Negative slope of blood lipids and positive slope of TG linear regression in Standardbred trotters were significant for all parameters (P ≤ .05), whereas cholesterol and LDL regression showed poor P and r² values and HDL P value was slightly above the significance level (P = .069) in Thoroughbred horses. TGs and VLDL showed a positive linear trend in Thoroughbred horses (P = .002). Exercise and different training programs lead to significant variations of lipid profile and lipid utilization in horses. Lipid utilization as an energy source improved with training in Standardbred trotters, whereas this was not the case in Thoroughbred horses. Further studies on the effect of training programs using different conditions and horse breeds would be necessary to understand lipid utilization as an energy source in athletic horses.     

Evaluation of Injectable Sustained Release Progestin Formulations for Suppression of Estrus and Ovulation in Mares

Thirty-one mares were used in an experiment to evaluate the effectiveness of three sustained-release injectable formulations of altrenogest and one formulation of medroxyprogesterone acetate (MPA) for long-term suppression of estrus and ovulation. Luteolysis was induced by injection of prostaglandin-F_2α (Lutalyse) on day 0 (6th day after the previous ovulation) and was immediately followed by treatment with 1) no injection (controls; n = 7), 2) 1.5 mL of an altrenogest solution in sustained-release vehicle (LA 150, 1.5 mL; 225 mg altrenogest; n = 6), 3) 3 mL (450 mg altrenogest) of the same solution (n = 6), 4) 500 mg altrenogest in lactide-glycolide microparticles suspended in 7-mL vehicle (MP 500; n = 6), or 5) 1.0 g MPA as a 5-mL suspension. Mares were checked for estrus daily, and their ovaries scanned every other day until a 25-mm or greater follicle was detected, after which they were scanned daily. Control mares returned to estrus an average of 3.9 days after Lutalyse administration; all the single-injection altrenogest formulations increased (P < .05) the days to return to estrus, with the greatest increase occurring in mares receiving MP 500. Return to estrus was not affected by MPA treatment. Time of ovulation was determined by serial ultrasound scans and confirmed by daily plasma luteinizing hormone (LH) and progesterone concentrations. Control mares ovulated an average of 8.8 days after Lutalyse administration. Treatment with 1.5 or 3 mL of LA 150 increased (P < .05) the mean days to ovulation to 16.5 and 21.2 days, respectively; MP 500 increased (P < .05) the days to ovulation to 33.5 days. Administration of MPA did not affect (P > .1) days to ovulation relative to control mares. The MP 500 treatment provided long-term suppression of estrus and ovulation and could prove useful for that purpose. Treatment with the LA 150 solutions provided shorter-term suppression, and a relatively tight grouping of the individual mares around the mean days to ovulation; these one-shot formulations could be useful for synchronizing ovulation in cyclic mares and inducing normal estrous cyclicity in vernal transitional mares exhibiting erratic, anovulatory estrous periods.     

Plasma concentrations and effects of glucagon-like peptide-1 (7-36) amide in calves before and after weaning

Glucagon-like peptide-1 (7-36) amide (GLP-1), secreted by the small intestine, has insulinotropic and glucose-lowering action. Basal plasma GLP-1 concentrations were measured in calves around the weaning period, the effect of short-chain fatty acids (SCFA) on plasma GLP-1 concentrations was examined, and the effects of GLP-1 administration on plasma insulin, glucagon, and glucose concentrations were measured. Thirteen Holstein bull calves were fed whole milk and solid feed and weaned at 7 wk of age. Preprandial plasma samples were obtained from 5 calves once a week from week 0 to 13 to measure basal concentrations of plasma GLP-1 and insulin (experiment 1). Four calves were intravenously administered with a mixed solution of SCFA (2.4 mmol/kg body weight [BW]) in week 2 and 11 to measure plasma GLP-1 concentrations (experiment 2). Another 4 calves were intravenously injected with GLP-1 (1.0 μg/kg BW) to elucidate the response of plasma insulin, glucagon, and glucose concentrations in week 1, 2, 4, 6, 7, 9, 11, and 13 (experiment 3). In experiment 1, age and weaning did not affect preprandial basal concentrations of plasma GLP-1 throughout the experimental period. Preprandial insulin concentrations increased after weaning (P < 0.05), and GLP-1 and insulin were more strongly correlated postweaning than preweaning. In experiment 2, intravenous treatment with SCFA increased plasma GLP-1 concentrations in both week 2 and 11 (P < 0.05.) In experiment 3, intravenous GLP-1 treatment decreased plasma glucose concentrations throughout the experiment (P < 0.05), but increased plasma insulin concentrations only after weaning (P < 0.05). Treatment with GLP-1 did not affect plasma glucagon concentrations, regardless of age. These results indicate that preprandial basal concentrations of plasma GLP-1 in calves are not changed by weaning, but SCFA stimulate GLP-1 secretion. The insulinotropic action of GLP-1 is detected only after weaning, but the glucose-lowering action of GLP-1 is not affected by weaning.